A process for the electrolysis of an aqueous solution of hydrogen chloride is disclosed e.g. in U.S. Pat. No. 5,770,035. An anode compartment with a suitable anode, comprising e.g. a substrate of a titanium/palladium alloy which is coated with a mixed oxide of ruthenium, iridium and titanium, is filled with the aqueous solution of hydrogen chloride. The chlorine formed at the anode escapes from the anode compartment and is fed to a suitable recovery process. The anode compartment is separated from the cathode compartment by a commercially available cation exchange membrane. On the cathode side, a gas diffusion electrode is mounted on the cation exchange membrane. The gas diffusion electrode in its turn is mounted on a current distributor. Gas diffusion electrodes are, for example, oxygen depletion cathodes (ODC). When using an ODC as a gas diffusion electrode, air, oxygen-enriched air or pure oxygen is normally introduced into the cathode compartment and this is reduced on the ODC.
Commercially available ion exchange membranes have a flat support structure of a woven fabric, gauze, braiding or the like made from e.g. polytetrafluoroethylene (PTFE), to one face of which is applied a perfluorosulfonic acid polymer such as e.g. Nafion®, a commercial product from DuPont. If this type of ion exchange membrane is used in an electrolysis cell with a gas diffusion electrode as an oxygen depletion cathode for the electrolysis of an aqueous solution of hydrogen chloride, a relatively high operating voltage, in the region of 1.25 to 1.3 V at 5 kA/m2, is required.